Conventionally, as an apparatus for blending an odor by mixing multiple component odor gases, there can be mentioned an apparatus in which predetermined amounts of component odor gases are supplied from respective supply sources through respective mass flow controllers, and a blend is made (Patent Document 1). In this apparatus, expensive mass flow controllers are required as many as the number of the types of component odor gas, and thus there is a problem that the entire cost becomes high as the number of types of component odor gas increases.
Accordingly, the present inventors proposed an apparatus in which inexpensive 3-way solenoid valves are used instead of mass flow controllers, an opening and closing frequency of the solenoid valve is controlled by ΔΣ modulation method, and the component odor gases with desired concentrations are supplied, for blending an odor (Patent Document 2). With respect to this apparatus, descriptions will be made with reference to FIGS. 15 and 16. Herein, FIG. 15 is a diagram showing a structure of an odor blender described in Patent Document 2, and FIG. 16 is a diagram illustrating modes of opening and closing of the 3-way solenoid valve by ΔΣ modulation.
The apparatus shown in FIG. 15 is an odor blender in which an odor of an odor gas of interest (target odor gas) is measured, and a mixing ratio (recipe) of two component odor gases is determined for reproducing the odor of the target odor gas. As shown in FIG. 15, the apparatus includes: carrier gas containers 1017 and 1021; a sample container 1018 for the target odor gas; component odor gas containers 1019 and 1020; a solenoid valve 1027; 3-way solenoid valves 1028a, 1028b, 1029a and 1029b; a sensor cell 1030; valved flowmeters 1040 and 1041; a suction pump 1031; a frequency counter 1032; and a computer 1033.
In this apparatus, the sensor cell 1030 has multiple QCM (Quartz Crystal Microbalance) sensors 1030A, 1030B . . . . Outputs of the QCM sensors are measured by the frequency counter 1032, and the measured values (sensor output vectors) are transmitted to the computer 1033. With these sensor outputs, the odor can be quantitatively determined.
A measurement system of this apparatus is a gas flow measurement system, and either the carrier gas (air, dry air or the like) or the target odor gas is supplied to the sensor cell 1030 at a constant flow rate. The gas flow is driven by the suction pump 1031 through the valved flowmeter 1040.
First, a target odor gas with which an odor is to be recorded is charged in the sample container 1018, and by opening the solenoid valve 1027, the target odor gas is supplied to the sensor cell 1030, where the odor is measured. The measured value (sensor output vector) is stored in the computer 1033. After the completion of the measurement, the solenoid valve 1027 is closed and the supply of the target odor gas is stopped. The opening and closing for each of the solenoid valve 1027 and the 3-way solenoid valves 1028a, 1028b, 1029a and 1029b is controlled by the computer 1033.
Next, by controlling the frequency of the opening and closing of the 3-way solenoid valves 1028a and 1028b, component odor gases with predetermined concentrations are supplied from the component odor gas containers 1019 and 1020 to the sensor cell 1030 to thereby blend an odor. The sensor output vectors of the blended odor are measured using the QCM sensors 1030A, 1030B . . . as well as the frequency counter 1032, and the computer 1033 compares the measured vectors with the sensor output vectors of the target odor. Based on a result of this comparison, the computer 1033 calculates a concentration of each component odor gas to be supplied, and in accordance with the calculated concentration, alters the frequency of the opening and closing of the 3-way solenoid valves 1028a and 1028b. 
FIG. 16 shows modes of the opening and closing of the 3-way solenoid valves 1028a and 1028b by ΔΣ modulation. As shown in A and B in the drawing, the opening and closing of the 3-way solenoid valves 1028a and 1028b is controlled in every short time period, such as about several ms to 100 ms. The time period indicated as a shaded area means a time period in which the corresponding component odor gas is supplied to the sensor cell 1030, and there are three modes including: a mode in which the component odor gases A and B are supplied to the sensor cell 1030 at the same time; a mode in which only one of the component odor gas is supplied, and a mode in which neither of them is supplied. Therefore, supply amount may change depending on the opening and closing state of the solenoid valves 1028a and 1028b. In addition, since the control is made in every short time period, it is difficult to accurately synchronize the solenoid valves 1028a and 1028b. 
In order to stably generate a blended odor regardless of the connection mode of the component odor gas containers 1019 and 1020 with the sensor cell 1030, the flow rate of the gas supply to the sensor cell 1030 should be constant. Accordingly, relative to the component odor gas containers 1019 and 1020, the corresponding carrier gas containers 1017 and 1021 are provided, and by controlling the 3-way solenoid valves 1028a and 1029a (1028b and 1029b) as a pair, a structure is made in which either the component odor gas or the carrier gas is supplied at the same flow rate to the sensor cell 1030, from each pair of the component odor gas container and carrier gas container. Further, in order to retain the gas concentration of the component odor in each headspace of the component odor gas containers 1019 and 1020 constant, the 3-way solenoid valves are used as a solenoid valve, and when the 3-way solenoid valves 1028a and 1028b are in a closed mode (in which the component odor gas is not supplied to the sensor cell 1030), the containers are connected to a gas flow line driven by the suction pump 1031 through the valved flowmeter 1041 (hereinafter, referred to as “bypass line”), to thereby retain the flow rates in the component odor gas containers 1019 and 1020 constant. With respect to the carrier gas containers each of which makes a pair with the corresponding component odor gas container, a symmetrical configuration similar to that of the component odor gas containers is made, and from each pair of the component odor gas container and the carrier gas container, the component odor gas and the carrier gas are supplied to the sensor cell 1030 and the bypass line in a complementary manner.
(Patent Document 1)
    Japanese patent publication No. 3331371A (paragraph 0019 and FIG. 1)(Patent Document 2)    Japanese patent publication No. 3722000 (paragraphs 0021 to 0027 and FIG. 2)